Free cutting alloys



Patented Apr. 13, 1937 UNITED STATES PATENT OFFICE FREE CUTTING ALLOYS Louis W. Kempf and Walter A. Dean, Cleveland,

Ohio, assignors to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application December 5, 1936, Serial N- 114,431

5 Claims. (Cl. 75-142) the making of so-called screw machineproducts. These products, which are generally of small dimensions, are turned out in large numbers on automatic machines. In order to make the articles in large quantities, the material from which they are made must be readily machinable; that is, the metal must out easily, form small, easily breakable chips which drop away from the cutting tool, and a pleasing, smooth surface must be left on the article. In addition, the alloy must possess sumcient strength to withstand the stresses incident to the machining operation and ultimate service. Since many of the screw machine products are comparatively small, it is particularly desirable that they be made from a strong material which will permit as great a ratio between the length and diameter as possible. For',this reason, wrought alloys which have been solution heat treated and aged are pre- 30 ferred. The best machining alloys of this type which have been developed to date are those which must be artificially aged; that is, reheated to 200 to 350 F. after being quenched from the solution heat treating temperature, to produce 35 the maximum strength. Such alloys as a rule are more brittle than those which age harden spontaneously at room temperatures, and this brittleness in turn serves to reduce the ratio be-. tween length and diameter of the machined arti- 40 ole that can be safely used. The necessity of reheating the alloys to artificially age them also adds to the cost of making articles. It is accordingly an object of our invention to provide an alloy which possesses excellent ma- 45 chining characteristics and is at thesame time spontaneously age hardenable after solution heat treatment. Another object is to provide a heat treated and aged alloy whose physical properties are substantially unimpaired by the addition of elements designed to improve the machinability. A further object is to provide aspontaneously age-hardenable aluminum base alloy which is adapted to the manufacture of screw machine products.

We have discovered that the addition of magnesiuin and at least one of the group of elements composed of nickel and cobalt, to a wrought aluminum base alloy containing from about 3.5 to 7 per cent copper, 0.1 to 1.5 percent lead and 0.1 to 1.5 per cent bismuth, renders the alloy spontaneously age hardenable after solution treatment without any loss in the free cutting,

qualities; The base alloy of alumlnum copper, lead and bismuth claimed in our formerly copending application, 'Serial No. 52,667, filed December 3, 1935, but now issued as United States Patent No. 2,047,873, has free cutting properties by virtue of the presence of both lead and hismuth. For our present purpose, from about 0.05 to 1.5 per cent magnesium and between 0.05 and 2.5 per cent'of at least one of the elements nickel and cobalt should be used in the alloy. If more than one of the two latter elements are to be employed, the total amountshould not exceed about 2.5 per' cent. In our preferred practice, we use from about 4.5 to 5.5 per cent of copper, from 0.2 to 0.8 per cent of lead, and from 0.2 to-0.8 per cent of bismuth, from 0.1 to 0.7 per cent of magnesium, from about 0.1 to 0.6 per cent of at least one of the elements nickel and cobalt, the total amount of the latter two elements not exceeding about 0.75 per cent.

The combined effect of magnesium and the group of elements composed of nickel and cobalt in making the alloy both age hardenable at ordinary temperatures after solution treatment and readily machinable, is surprising in view of the' .behavior of each element alone in the same base alloy. Magnesium, for example, has been widely used in heat treated aluminum base alloy because of its favorable effect upon the properties.

However, when this element is added to an aluminum base alloy containing about 5 per cent copper, 0.5 per cent lead and 0.5 per cent bismuth, the machinability is somewhat impaired, although the alloy will age harden at room temperature. Since the base alloy of aluminum, 5 per cent copper, 0.5 percent lead and-0.5 per cent bismuth, is readily machinable and is rated as a free cutting alloy, any additions thereto which adversely affect this property are undesirable.

0n the other hand, the presence of nickel or cobalt in some aluminum base alloys has been observed to improve the machinability, but when these elements are added to an alloy of aluminum 5 per cent copper, 0.5 per cent lead and 0.5 per cent bismuth, the machining quality is adversely affected. From this standpoint, therefore, the addition of nickel or cobalt is of no value.

tests that the presence oi. both nickel and/r cobalt and magnesium has the surprising effect of making the aluminum-co'pper-lead-bismuth alloy spontaneously ageable after solution heat treatment without detracting in any way from the machinabllity of the alloy. The improved alloy machine's withsmalllchlps which drop away; from the cutting tool, and a smooth, pleasing sur- 1 face is left on the machined article such as is,

desired in screw machine products. Furthermore, the presence of magnesium and nickel or cobalt does not increase the wear on the cutting t l :Ti' I The elements nickel and cobalt constitute a group of substances which have-a similar eil'ect in an aluminum-copperlead-bismuth alloy in the presence of magnesium. For the'purpose of our invention, these two elements constitute a cases, the alloys were forged from billets to rod 35 form, heat treated at 940 F., and quenched in water. The artificial aging consisted in reheating to 310 F..i'or l6-hours. In each case, the base alloy is the same; namely, aluminum, 5 per cent. copper, 0.5 per cent lead and 0 5 per cent bismuth.

ea; u 8 ten 11 P Al- Aging B. H. by Addedelements mp 581211;. N

' Hounds per sq. inch A None Room 39,400 14,000 24.5 66 A None. 310"! 54,000 00,000 10.0 100 B 0.5 Mg0.25 00. Room 52,200 20,200 10.5 05 c 0510 0.25 Ni- Room 53,100 30,300 11.0 101 50 The solution heat treatment to which our improved alloy isto be subjected is to the usual type; namely, heating ata temperature between about u 2,070,080 We have now determined by a number of 900 and 980 F. fora .period of 5 minutes to y 10 hours, depending on the means of heating and mass or metal to be heated. The alloy is to be rapidly cooled from the heating tempera ture as. by' quenching in water, and then allowed to stand for several days to attain full strengthv and hardness by virtue of the spontaneous age hardening which occurs at room temperatures. The alloy in the aged condition is ready for machining. u 1

The term aluminum as herein employed, refers to the metal of commercial grade which contains the impurities iron and silicon.

We claim:

1. An aluminum base alloy consisting of from about 3.5 to '7 percent copper, about 0.1 to 1.5 per cent lead, about 0.1 to 1.5 per cent bismuth, about 0.05 to 1.5 per cent magnesium and from about 0.05 to 2.5 per cent of at least one of the group of elements composed of nickel and cobalt, the total amount of said elements not exceeding about 2.5 per cent, the balance of the alloy being aluminum.

2. An aluminum base alloy consisting of irom about 4.5 to 5.5 per cent copper, about 0.2 to 0.8-

per cent lead, about 0.2 'to-0..per cent bismuth, about 0.1 to 0.7 per cent magnesium, and from about 0.1 to 0.6 per cent of at least one of the group of elements composed of nickel and cobalt, the total amount of said elements not exceeding about 0.75 per cent, the balance 01' the alloy being aluminum.

3. An aluminum base alloycontaining from about 3.5 to? per cent copper,\ about-0.1 to 1.5

per cent lead, about 0.1 to 1.5 per cent bismuth, about 0.05 to 1.5 per centmagnesium and from about 0.05 to 2.5 percent of at least one 01' the group of elements composed of nickel and cobalt,

the total amount of said elements not exceeding about 2.5 per. cent, said alloy being characterized by being free cutting and spontaneously age hardenable after solution heat treatment.

4.. An aluminum base alloy composed 01 about 5 per cent copper, 0.5 per cent lead, 0.5 per cent bismuth, 0.5 per cent magnesium and 0.25 per cent nickel, and the balance aluminum.

5. An aluminum base alloy composed of about 5 per cent copper, 0.5 per cent lead, 0.5 per cent bismuth, 0.5 per cent magnesium and 0.25 per cent cobalt, and the balance aluminum.

- LOUIS W. KEMPF. WALTER A. DEAN. 

